Passives

VPG unveil ultra-high-precision Z-Foil Power Current Sensing Resistors

12th July 2013
ES Admin
Vishay Precision Group has released two new ultra-high-precision hermetically sealed Z-Foil power current sensing resistors with low TCR of ±0.2 ppm/°C (from -55°C to +125°C, +25°C ref.), PCR of 4 ppm/W typical, and tolerances to ±0.01%. Designed to provide optimal performance when mounted on a chassis or cooled heat sink, the hermetically sealed VHP4Z and VPR247Z offer power ratings of 10 W (heat sink) and 3 W (free air), and a four-terminal Kelvin configuration for increased accuracy in high-power applications.
The VHP4Z and VPR247Z offer a welded construction and a screw-mount for direct attachment to a metal heat sink. Hermetic sealing and a nitrogen back-fill for the VPR247Z provide maximum protection against environmental stresses to ensure long-term stability.

Ideal for applications such as test and measurement where rapid ΔR stabilization and resistance stability under transient power conditions are required, the devices offer excellent load-life stability down to ±0.005% typical (50 ppm) at 3 W (heat sink) at +25°C for 2,000 hours. While the VHP4Z's copper leads provide low thermal EMF, the VPR247Z provides a significantly reduced size and weight and features gold-plated copper leads for higher stability.

The VHP4Z and VPR247Z offer a thermal stabilization time of <1 s (within 10 ppm of steady state value) and a wide resistance range from 0.25 Ω to 500 Ω. Any resistance value within this range is available at any tolerance with no additional cost or lead time effect. The resistors offer a rise time of 1.0 ns with effectively no ringing, current noise of 0.010 µVrms/V of applied voltage (<-40 dB), and a voltage coefficient of <0.1 ppm/V. The devices withstand ESD to at least 25 kV, for increased reliability, and offer a non-inductive (<0.08 μH), non-capacitive design.

The VHP4Z and VPR247Z are based on our expertise in stress analysis and proprietary methods of manufacturing precision 4-terminal resistors, said Yuval Hernik, Senior Director of Application Engineering for VFR. Their use of Z-Foil technology allows them to achieve a very low TCR and PCR over a very wide temperature range. And since this important specification is also influenced by the application's assembly methods, anticipated current fluctuations, and accuracy and response time requirements, we are available to collaborate with our customers on their designs for the most efficient design process.

Every current sense resistor must have an error budget assigned to it which, if exceeded, will cause the equipment to fall out of its performance specification, or possibly fail. In addition to initial tolerance, the error budget includes allowable shifts through shelf life, assembly, TCR, shock, vibration, humidity exposure, thermal shock, thermal EMF, load-life drift, ESD, radiation, and harmonic distortion. The VHP4Z and VPR247Z are the perfect choice to accomplish the lowest total end-of-life tolerance band.

Samples and production quantities of the VHP4Z and VPR247Z are available now, with lead times of five working days for samples and eight weeks for larger orders.

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